1. Field of the Invention
The present invention relates to an electrostatic charged particle beam lens and a charged particle beam exposure apparatus using the same.
2. Description of the Related Art
In the production of a semiconductor device, electron beam exposure technology is prospective for lithography which enables fine pattern exposure of 0.1 μm or less. In an electron beam exposure apparatus, an electron-optical element for controlling optical characteristics of an electron beam is used.
In the electron beam exposure technology, for the purpose of attaining finer exposure, both high voltage application to an electron lens and thinning of the lens are required, and a high withstand voltage structure is necessary.
Further, in the electron beam exposure technology, the limit of fine processing is determined mainly by the optical aberration of the electron-optical element rather than by the diffraction limit of the electron beam, and thus, it is important to realize an electron-optical element having small aberration.
In order to attain this, first of all, the accuracy of the shape of the processed lens is required to be at a high level. For example, in order to stabilize fine pattern exposure on the order of 0.1 μm or less, the accuracy of the shape is required to be on the order thereof or finer.
Further, optical aberration is caused also by charge of members of the lens.
Further, in the electron beam exposure technology, contamination to be generated through application of the electron beam to a resist, that is, contamination ascribable to the resist is inevitable.
Contamination adhesion to the electron-optical system, such as the electron lens, causes deterioration of the shape of an opening in the lens and causes a charged state, which degrades the aberration and the withstand voltage.
In order to stabilize stable fine processing, measures against contamination are important. Japanese Patent No. 3166946 discloses a structure of an electron beam exposure apparatus in which a conductive plate-shaped body is provided between a sample and an objective lens for condensing an electron beam for the purpose of reducing charge by means of preventing or reducing adhesion of contamination, including a substance evaporated from the surface of the sample to the objective lens, and an electron beam deflector.
On the other hand, in order to reduce adhesion of contamination ascribable to the resist, it is effective to improve the vacuum to reduce the density of the contamination.
Japanese Patent No. 4401614 discloses a structure in which dummy openings are provided.
This structure is thought to be effective in reducing contamination adhesion, but, in this literature, the object is to make uniform focal points of multiple electron beams with respect to an object of the application for the purpose of exposing a pattern on the object of the application with accuracy. If the structure is used as it is, the effect against contamination adhesion, especially, around the center of the lens is thought to be small.
On the other hand, with regard to a method of removing contamination that has once adhered, generally, contamination is removed by plasma treatment or heat treatment.
However, with regard to an array of electron lenses, in particular, objective lenses, or the like, which include complex members and require that high accuracy of the shape thereof, the latter method is hardly used from the viewpoint of deformation and damage.
Further, in the electron beam exposure technology, realization of higher throughput is one of large issues, and a multi-beam system is nominated for one of the solutions for it.
In the multi-beam system, it has been proposed to use an electron lens array in which electron lenses are arranged in a one-dimensional or two-dimensional array.
When the multi-beam system is adopted, measures against charge are necessary from the viewpoint of reducing optical aberration. In particular, in an electron lens array, measures against charge of a distance defining member (insulator) between electrodes are necessary. General examples of such measures against charge include forming an antistatic film on an insulating member, and placing the insulator away from an opening in an electrode of a lens.
In order to accommodate the demand for finer exposure technology with higher throughput, in an electron beam exposure apparatus, reduction of the aberration and adoption of the multi-beam system are necessary.
Among electrostatic lenses, in particular, an objective lens is required to have a higher withstand voltage structure, and to improve the accuracy of the shape thereof, in order to reduce the distance between the lens and the work, to use a multi-beam system of electron beams, to reduce the diameter and the pitch of the openings, and to use a higher electric field.
On the other hand, when a sample is exposed using an electron beam, the energy of the beam causes the resist, or the like, on the sample to scatter or to evaporate.
The resist, or the like, which scatters or evaporates adheres more onto an objective lens that is the nearest to the sample.
As the exposure continues for a long time, the amount of the adhering substance becomes larger and the adhering substance accumulates. The optical aberration characteristics of the objective lens are very sensitive to the shape of the opening.
Therefore, as the adhering substance ascribable to the resist, such as the resist, or the like, which scatters or evaporates, or a substance produced therefrom, accumulates on the opening, the optical aberration characteristics of the objective lens degrade accordingly.
Degradation of the optical aberration characteristics of the objective lens due to accumulation of such an adhering substance is a problem, and thus, as a solution for it, cleaning treatment of the lens is necessary.
In particular, the optical aberration characteristics are most sensitive to an intermediate electrode sandwiched between an upper electrode and a lower electrode of an objective lens, and the effect of cleaning treatment with regard to the intermediate electrode against the adhering substance ascribable to the resist, which is accumulated, is the smallest from the viewpoint of the structure, which is a problem.